This project involves a continuing study of the actions of organophosphorus pesticides on developing chick skeletal muscle and other tissues. Current research emphasizes embryo acetylcholinesterase (AChE) isozymes and the actions of the organophosphorus agents that inhibit them using tissues, muscle and muscle-nerve cultures. Little is known concerning these enzymes. We have demonstrated that AChE isozymes localized in the sarcoplasm of embryo muscle are suppressed by neural activity after hatching. They reappear in denervated muscle and are maintained in muscles with inherited and nutritional muscular dystrophy. Recent research indicates similar isozymes occur in fetal human muscle. Studies are underway with chick embryo muscle to elucidate the role and regulation of these embryo AChE forms and examine the effects of organophosphorous agents on the development of embryo muscle. Emphasis will be given to possible "neurotrophic" controls and the organophosphorus agents malathion, parathion and related compounds. Biochemical, light and electron microscopy studies will be performed emphasizing primary cell cultures of muscle, nerve and their tissues of origin.